diff --git a/include/helix/helix.hh b/include/helix/helix.hh
index 2324302..70700e8 100644
--- a/include/helix/helix.hh
+++ b/include/helix/helix.hh
@@ -29,8 +29,6 @@ public:
     { }
 };
 
-namespace core {
-
 enum class trade_sign {
     buyer_initiated,
     seller_initiated,
@@ -99,7 +97,7 @@ public:
 
     virtual void subscribe(const std::string& symbol, size_t max_orders) = 0;
 
-    virtual void register_callback(core::event_callback callback) = 0;
+    virtual void register_callback(event_callback callback) = 0;
 
     virtual size_t process_packet(const net::packet_view& packet) = 0;
 };
@@ -110,5 +108,3 @@ public:
 };
 
 }
-
-}
diff --git a/include/helix/nasdaq/binaryfile.hh b/include/helix/nasdaq/binaryfile.hh
index b68070c..aabc8c5 100644
--- a/include/helix/nasdaq/binaryfile.hh
+++ b/include/helix/nasdaq/binaryfile.hh
@@ -20,7 +20,7 @@ namespace helix {
 namespace nasdaq {
 
 template<typename Handler>
-class binaryfile_session : public core::session {
+class binaryfile_session : public session {
     Handler _handler;
 public:
     explicit binaryfile_session(void* data);
@@ -29,7 +29,7 @@ public:
 
     virtual void subscribe(const std::string& symbol, size_t max_orders) override;
 
-    virtual void register_callback(core::event_callback callback) override;
+    virtual void register_callback(event_callback callback) override;
 
     virtual size_t process_packet(const net::packet_view& packet) override;
 };
@@ -53,7 +53,7 @@ void binaryfile_session<Handler>::subscribe(const std::string& symbol, size_t ma
 }
 
 template<typename Handler>
-void binaryfile_session<Handler>::register_callback(core::event_callback callback)
+void binaryfile_session<Handler>::register_callback(event_callback callback)
 {
     _handler.register_callback(callback);
 }
diff --git a/include/helix/nasdaq/itch50_handler.hh b/include/helix/nasdaq/itch50_handler.hh
index 6c4a9ba..8ecf16e 100644
--- a/include/helix/nasdaq/itch50_handler.hh
+++ b/include/helix/nasdaq/itch50_handler.hh
@@ -29,9 +29,9 @@ namespace nasdaq {
 class itch50_handler {
 private:
     //! Callback function for processing events.
-    core::event_callback _process_event;
+    event_callback _process_event;
     //! A map of order books by order book ID.
-    std::unordered_map<uint64_t, helix::core::order_book> order_book_id_map;
+    std::unordered_map<uint64_t, helix::order_book> order_book_id_map;
     //! A set of symbols that we are interested in.
     std::set<std::string> _symbols;
     //! A map of pre-allocation size by symbol.
@@ -40,7 +40,7 @@ public:
     itch50_handler();
     bool is_rth_timestamp(uint64_t timestamp) const;
     void subscribe(std::string sym, size_t max_orders);
-    void register_callback(core::event_callback callback);
+    void register_callback(event_callback callback);
     size_t process_packet(const net::packet_view& packet);
 private:
     template<typename T>
@@ -66,7 +66,7 @@ private:
     void process_msg(const itch50_noii* m);
     void process_msg(const itch50_rpii* m);
     //! Generate a sweep event if execution cleared a price level.
-    core::event_mask sweep_event(const core::execution&) const;
+    event_mask sweep_event(const execution&) const;
 };
 
 }
diff --git a/include/helix/nasdaq/itch50_protocol.hh b/include/helix/nasdaq/itch50_protocol.hh
index 589fb5a..c1b25d8 100644
--- a/include/helix/nasdaq/itch50_protocol.hh
+++ b/include/helix/nasdaq/itch50_protocol.hh
@@ -8,12 +8,12 @@ namespace helix {
 
 namespace nasdaq {
 
-class itch50_protocol : public core::protocol {
+class itch50_protocol : public protocol {
     std::string _name;
 public:
     explicit itch50_protocol(std::string name);
     static bool supports(const std::string& name);
-    virtual core::session* new_session(void *) override;
+    virtual session* new_session(void *) override;
 };
 
 }
diff --git a/include/helix/nasdaq/moldudp.hh b/include/helix/nasdaq/moldudp.hh
index 3bb2bab..b064840 100644
--- a/include/helix/nasdaq/moldudp.hh
+++ b/include/helix/nasdaq/moldudp.hh
@@ -28,7 +28,7 @@ namespace helix {
 namespace nasdaq {
 
 template<typename Handler>
-class moldudp_session : public core::session {
+class moldudp_session : public session {
     Handler _handler;
     uint32_t _seq_num;
 public:
@@ -38,7 +38,7 @@ public:
 
     virtual void subscribe(const std::string& symbol, size_t max_orders) override;
 
-    virtual void register_callback(core::event_callback callback) override;
+    virtual void register_callback(event_callback callback) override;
 
     virtual size_t process_packet(const net::packet_view& packet) override;
 
@@ -64,7 +64,7 @@ void moldudp_session<Handler>::subscribe(const std::string& symbol, size_t max_o
 }
 
 template<typename Handler>
-void moldudp_session<Handler>::register_callback(core::event_callback callback)
+void moldudp_session<Handler>::register_callback(event_callback callback)
 {
     _handler.register_callback(callback);
 }
diff --git a/include/helix/nasdaq/moldudp64.hh b/include/helix/nasdaq/moldudp64.hh
index b820255..6a8c4cc 100644
--- a/include/helix/nasdaq/moldudp64.hh
+++ b/include/helix/nasdaq/moldudp64.hh
@@ -21,7 +21,7 @@ namespace helix {
 namespace nasdaq {
 
 template<typename Handler>
-class moldudp64_session : public core::session {
+class moldudp64_session : public session {
     Handler _handler;
     uint64_t _seq_num;
 public:
@@ -31,7 +31,7 @@ public:
 
     virtual void subscribe(const std::string& symbol, size_t max_orders) override;
 
-    virtual void register_callback(core::event_callback callback) override;
+    virtual void register_callback(event_callback callback) override;
 
     virtual size_t process_packet(const net::packet_view& packet) override;
 };
@@ -56,7 +56,7 @@ void moldudp64_session<Handler>::subscribe(const std::string& symbol, size_t max
 }
 
 template<typename Handler>
-void moldudp64_session<Handler>::register_callback(core::event_callback callback)
+void moldudp64_session<Handler>::register_callback(event_callback callback)
 {
     _handler.register_callback(callback);
 }
diff --git a/include/helix/nasdaq/nordic_itch_handler.hh b/include/helix/nasdaq/nordic_itch_handler.hh
index 5a2ccf7..7878b1d 100644
--- a/include/helix/nasdaq/nordic_itch_handler.hh
+++ b/include/helix/nasdaq/nordic_itch_handler.hh
@@ -39,11 +39,11 @@ class nordic_itch_handler {
     //! Milliseconds since @time_sec.
     uint64_t time_msec;
     //! Callback function for processing events.
-    core::event_callback _process_event;
+    event_callback _process_event;
     //! A map of order books by order book ID.
-    std::unordered_map<uint64_t, helix::core::order_book> order_book_id_map;
+    std::unordered_map<uint64_t, helix::order_book> order_book_id_map;
     //! A map of order books by order ID.
-    std::unordered_map<uint64_t, helix::core::order_book&> order_id_map;
+    std::unordered_map<uint64_t, helix::order_book&> order_id_map;
     //! A set of symbols that we are interested in.
     std::set<std::string> _symbols;
     //! A map of pre-allocation size by symbol.
@@ -52,7 +52,7 @@ public:
     nordic_itch_handler();
     bool is_rth_timestamp(uint64_t timestamp) const;
     void subscribe(std::string sym, size_t max_orders);
-    void register_callback(core::event_callback callback);
+    void register_callback(event_callback callback);
     size_t process_packet(const net::packet_view& packet);
 private:
     template<typename T>
@@ -74,7 +74,7 @@ private:
     void process_msg(const itch_broken_trade* m);
     void process_msg(const itch_noii* m);
     //! Generate a sweep event if execution cleared a price level.
-    core::event_mask sweep_event(const core::execution&) const;
+    event_mask sweep_event(const execution&) const;
     //! Timestamp in milliseconds
     uint64_t timestamp() const;
 };
diff --git a/include/helix/nasdaq/nordic_itch_protocol.hh b/include/helix/nasdaq/nordic_itch_protocol.hh
index b4409c4..0f74ce8 100644
--- a/include/helix/nasdaq/nordic_itch_protocol.hh
+++ b/include/helix/nasdaq/nordic_itch_protocol.hh
@@ -8,12 +8,12 @@ namespace helix {
 
 namespace nasdaq {
 
-class nordic_itch_protocol : public core::protocol {
+class nordic_itch_protocol : public protocol {
     std::string _name;
 public:
     static bool supports(const std::string& name);
     explicit nordic_itch_protocol(std::string name);
-    virtual core::session* new_session(void *) override;
+    virtual session* new_session(void *) override;
 };
 
 }
diff --git a/include/helix/nasdaq/soupfile.hh b/include/helix/nasdaq/soupfile.hh
index e89ae6f..b08d1bf 100644
--- a/include/helix/nasdaq/soupfile.hh
+++ b/include/helix/nasdaq/soupfile.hh
@@ -18,7 +18,7 @@ namespace helix {
 namespace nasdaq {
 
 template<typename Handler>
-class soupfile_session : public core::session {
+class soupfile_session : public session {
     Handler _handler;
 public:
     explicit soupfile_session(void* data);
@@ -27,7 +27,7 @@ public:
 
     virtual void subscribe(const std::string& symbol, size_t max_orders) override;
 
-    virtual void register_callback(core::event_callback callback) override;
+    virtual void register_callback(event_callback callback) override;
 
     virtual size_t process_packet(const net::packet_view& packet) override;
 };
@@ -51,7 +51,7 @@ void soupfile_session<Handler>::subscribe(const std::string& symbol, size_t max_
 }
 
 template<typename Handler>
-void soupfile_session<Handler>::register_callback(core::event_callback callback)
+void soupfile_session<Handler>::register_callback(event_callback callback)
 {
     _handler.register_callback(callback);
 }
diff --git a/include/helix/order_book.hh b/include/helix/order_book.hh
index 944d208..11c27d4 100644
--- a/include/helix/order_book.hh
+++ b/include/helix/order_book.hh
@@ -21,8 +21,6 @@
 
 namespace helix {
 
-namespace core {
-
 /// \addtogroup order-book
 /// @{
 
@@ -167,5 +165,3 @@ private:
 /// @}
 
 }
-
-}
diff --git a/include/helix/parity/pmd_handler.hh b/include/helix/parity/pmd_handler.hh
index 884300c..1205b23 100644
--- a/include/helix/parity/pmd_handler.hh
+++ b/include/helix/parity/pmd_handler.hh
@@ -26,11 +26,11 @@ namespace parity {
 //
 class pmd_handler {
     //! Callback function for processing events.
-    core::event_callback _process_event;
+    event_callback _process_event;
     //! A map of order books by order book ID.
-    std::unordered_map<std::string, helix::core::order_book> _order_book_id_map;
+    std::unordered_map<std::string, helix::order_book> _order_book_id_map;
     //! A map of order books by order ID.
-    std::unordered_map<uint64_t, helix::core::order_book&> _order_id_map;
+    std::unordered_map<uint64_t, helix::order_book&> _order_id_map;
     //! A set of symbols that we are interested in.
     std::set<std::string> _symbols;
     //! Number of seconds since midnight when the trading session started.
@@ -39,7 +39,7 @@ public:
     pmd_handler();
     bool is_rth_timestamp(uint64_t timestamp) const;
     void subscribe(std::string sym, size_t max_orders);
-    void register_callback(core::event_callback callback);
+    void register_callback(event_callback callback);
     size_t process_packet(const net::packet_view& packet);
 private:
     template<typename T>
@@ -52,7 +52,7 @@ private:
     void process_msg(const pmd_order_deleted* m);
     void process_msg(const pmd_broken_trade* m);
     //! Generate a sweep event if execution cleared a price level.
-    core::event_mask sweep_event(const core::execution&) const;
+    event_mask sweep_event(const execution&) const;
     uint64_t to_timestamp(uint64_t nanoseconds) const;
 };
 
diff --git a/include/helix/parity/pmd_protocol.hh b/include/helix/parity/pmd_protocol.hh
index d09b9f7..59c9326 100644
--- a/include/helix/parity/pmd_protocol.hh
+++ b/include/helix/parity/pmd_protocol.hh
@@ -11,13 +11,13 @@ namespace helix {
 
 namespace parity {
 
-class pmd_protocol : public core::protocol {
+class pmd_protocol : public protocol {
     std::string _name;
 public:
     static bool supports(const std::string& name);
 
     explicit pmd_protocol(std::string name);
-    virtual core::session* new_session(void *) override;
+    virtual session* new_session(void *) override;
 };
 
 }
diff --git a/src/event.cc b/src/event.cc
index a1bd044..f98523c 100644
--- a/src/event.cc
+++ b/src/event.cc
@@ -2,8 +2,6 @@
 
 namespace helix {
 
-namespace core {
-
 event::event(event_mask mask, uint64_t timestamp, order_book* ob, trade* t)
     : _mask{mask}
     , _timestamp{timestamp}
@@ -48,5 +46,3 @@ event make_trade_event(uint64_t timestamp, trade* t, event_mask mask)
 }
 
 }
-
-}
diff --git a/src/helix.cc b/src/helix.cc
index f901b4a..7103381 100644
--- a/src/helix.cc
+++ b/src/helix.cc
@@ -12,54 +12,54 @@
 
 using namespace std;
 
-inline helix_order_book_t wrap(helix::core::order_book* ob)
+inline helix_order_book_t wrap(helix::order_book* ob)
 {
     return reinterpret_cast<helix_order_book_t>(ob);
 }
 
-inline helix::core::order_book* unwrap(helix_order_book_t ob)
+inline helix::order_book* unwrap(helix_order_book_t ob)
 {
-    return reinterpret_cast<helix::core::order_book*>(ob);
+    return reinterpret_cast<helix::order_book*>(ob);
 }
 
-inline helix_trade_t wrap(helix::core::trade* ob)
+inline helix_trade_t wrap(helix::trade* ob)
 {
     return reinterpret_cast<helix_trade_t>(ob);
 }
 
-inline helix::core::trade* unwrap(helix_trade_t ob)
+inline helix::trade* unwrap(helix_trade_t ob)
 {
-    return reinterpret_cast<helix::core::trade*>(ob);
+    return reinterpret_cast<helix::trade*>(ob);
 }
 
-inline helix_event_t wrap(helix::core::event* ob)
+inline helix_event_t wrap(helix::event* ob)
 {
     return reinterpret_cast<helix_event_t>(ob);
 }
 
-inline helix::core::event* unwrap(helix_event_t ob)
+inline helix::event* unwrap(helix_event_t ob)
 {
-    return reinterpret_cast<helix::core::event*>(ob);
+    return reinterpret_cast<helix::event*>(ob);
 }
 
-inline helix_protocol_t wrap(helix::core::protocol* proto)
+inline helix_protocol_t wrap(helix::protocol* proto)
 {
     return reinterpret_cast<helix_protocol_t>(proto);
 }
 
-inline helix::core::protocol* unwrap(helix_protocol_t proto)
+inline helix::protocol* unwrap(helix_protocol_t proto)
 {
-    return reinterpret_cast<helix::core::protocol*>(proto);
+    return reinterpret_cast<helix::protocol*>(proto);
 }
 
-inline helix_session_t wrap(helix::core::session* session)
+inline helix_session_t wrap(helix::session* session)
 {
     return reinterpret_cast<helix_session_t>(session);
 }
 
-inline helix::core::session* unwrap(helix_session_t session)
+inline helix::session* unwrap(helix_session_t session)
 {
-    return reinterpret_cast<helix::core::session*>(session);
+    return reinterpret_cast<helix::session*>(session);
 }
 
 helix_protocol_t helix_protocol_lookup(const char *name)
@@ -80,8 +80,8 @@ helix_session_t
 helix_session_create(helix_protocol_t proto, helix_event_callback_t callback, void *data)
 {
     auto session = unwrap(proto)->new_session(data);
-    session->register_callback([session, callback](const helix::core::event& event) {
-        callback(wrap(session), wrap(const_cast<helix::core::event*>(&event)));
+    session->register_callback([session, callback](const helix::event& event) {
+        callback(wrap(session), wrap(const_cast<helix::event*>(&event)));
     });
     return wrap(session);
 }
@@ -178,7 +178,7 @@ helix_price_t helix_order_book_midprice(helix_order_book_t ob, size_t level)
 
 helix_trading_state_t helix_order_book_state(helix_order_book_t ob)
 {
-    using namespace helix::core;
+    using namespace helix;
     switch (unwrap(ob)->state()) {
     case trading_state::unknown:        return HELIX_TRADING_STATE_UNKNOWN;
     case trading_state::halted:         return HELIX_TRADING_STATE_HALTED;
@@ -213,10 +213,10 @@ uint64_t helix_trade_size(helix_trade_t trade)
 helix_trade_sign_t helix_trade_sign(helix_trade_t trade)
 {
     switch (unwrap(trade)->sign) {
-    case helix::core::trade_sign::buyer_initiated:  return HELIX_TRADE_SIGN_BUYER_INITIATED;
-    case helix::core::trade_sign::seller_initiated: return HELIX_TRADE_SIGN_SELLER_INITIATED;
-    case helix::core::trade_sign::crossing:         return HELIX_TRADE_SIGN_CROSSING;
-    case helix::core::trade_sign::non_displayable:  return HELIX_TRADE_SIGN_NON_DISPLAYABLE;
+    case helix::trade_sign::buyer_initiated:  return HELIX_TRADE_SIGN_BUYER_INITIATED;
+    case helix::trade_sign::seller_initiated: return HELIX_TRADE_SIGN_SELLER_INITIATED;
+    case helix::trade_sign::crossing:         return HELIX_TRADE_SIGN_CROSSING;
+    case helix::trade_sign::non_displayable:  return HELIX_TRADE_SIGN_NON_DISPLAYABLE;
     }
     assert(0);
 }
diff --git a/src/nasdaq/itch50_handler.cc b/src/nasdaq/itch50_handler.cc
index c891268..e11865f 100644
--- a/src/nasdaq/itch50_handler.cc
+++ b/src/nasdaq/itch50_handler.cc
@@ -13,7 +13,6 @@
 #include <memory>
 #include <string>
 
-using namespace helix::core;
 using namespace std;
 
 namespace helix {
@@ -70,7 +69,7 @@ void itch50_handler::subscribe(std::string sym, size_t max_orders) {
     order_book_id_map.reserve(max_all_orders);
 }
 
-void itch50_handler::register_callback(core::event_callback callback) {
+void itch50_handler::register_callback(event_callback callback) {
     _process_event = callback;
 }
 
diff --git a/src/nasdaq/itch50_protocol.cc b/src/nasdaq/itch50_protocol.cc
index c92ebab..d5b6c7b 100644
--- a/src/nasdaq/itch50_protocol.cc
+++ b/src/nasdaq/itch50_protocol.cc
@@ -17,7 +17,7 @@ itch50_protocol::itch50_protocol(std::string name)
 {
 }
 
-core::session* itch50_protocol::new_session(void *data)
+session* itch50_protocol::new_session(void *data)
 {
     if (_name == "nasdaq-binaryfile-itch50") {
         return new binaryfile_session<itch50_handler>(data);
diff --git a/src/nasdaq/nordic_itch_handler.cc b/src/nasdaq/nordic_itch_handler.cc
index ba6de2f..4759528 100644
--- a/src/nasdaq/nordic_itch_handler.cc
+++ b/src/nasdaq/nordic_itch_handler.cc
@@ -12,7 +12,6 @@
 #include <memory>
 #include <string>
 
-using namespace helix::core;
 using namespace std;
 
 namespace helix {
@@ -34,7 +33,7 @@ void nordic_itch_handler::subscribe(std::string sym, size_t max_orders)
     order_id_map.reserve(max_all_orders);
 }
 
-void nordic_itch_handler::register_callback(core::event_callback callback)
+void nordic_itch_handler::register_callback(event_callback callback)
 {
     _process_event = callback;
 }
diff --git a/src/nasdaq/nordic_itch_protocol.cc b/src/nasdaq/nordic_itch_protocol.cc
index 6b2f834..563ec6b 100644
--- a/src/nasdaq/nordic_itch_protocol.cc
+++ b/src/nasdaq/nordic_itch_protocol.cc
@@ -19,7 +19,7 @@ bool nordic_itch_protocol::supports(const std::string& name)
         || name == "nasdaq-nordic-soupfile-itch";
 }
 
-core::session* nordic_itch_protocol::new_session(void *data)
+session* nordic_itch_protocol::new_session(void *data)
 {
     if (_name == "nasdaq-nordic-moldudp-itch") {
         return new moldudp_session<nordic_itch_handler>(data);
diff --git a/src/order_book.cc b/src/order_book.cc
index 2d631d9..deeda6d 100644
--- a/src/order_book.cc
+++ b/src/order_book.cc
@@ -8,8 +8,6 @@ using namespace std;
 
 namespace helix {
 
-namespace core {
-
 execution::execution(uint64_t price, side_type side, uint64_t remaining)
     : price{price}
     , side{side}
@@ -225,5 +223,3 @@ uint64_t order_book::midprice(size_t level) const
 }
 
 }
-
-}
diff --git a/src/parity/pmd_handler.cc b/src/parity/pmd_handler.cc
index 4fefbe7..4303f30 100644
--- a/src/parity/pmd_handler.cc
+++ b/src/parity/pmd_handler.cc
@@ -12,7 +12,6 @@
 #include <memory>
 #include <string>
 
-using namespace helix::core;
 using namespace std;
 
 namespace helix {
@@ -48,7 +47,7 @@ bool pmd_handler::is_rth_timestamp(uint64_t timestamp) const
 
 void pmd_handler::subscribe(std::string sym, size_t max_orders)
 {
-    helix::core::order_book ob{sym, 0, max_orders};
+    helix::order_book ob{sym, 0, max_orders};
     ob.set_state(trading_state::trading);
     auto padding = PMD_INSTRUMENT_LEN - sym.size();
     if (padding > 0) {
@@ -58,7 +57,7 @@ void pmd_handler::subscribe(std::string sym, size_t max_orders)
     _order_book_id_map.emplace(sym, std::move(ob));
 }
 
-void pmd_handler::register_callback(core::event_callback callback)
+void pmd_handler::register_callback(event_callback callback)
 {
     _process_event = callback;
 }
diff --git a/src/parity/pmd_protocol.cc b/src/parity/pmd_protocol.cc
index 564940e..9120e30 100644
--- a/src/parity/pmd_protocol.cc
+++ b/src/parity/pmd_protocol.cc
@@ -17,7 +17,7 @@ pmd_protocol::pmd_protocol(std::string name)
 {
 }
 
-core::session* pmd_protocol::new_session(void *data)
+session* pmd_protocol::new_session(void *data)
 {
     return new nasdaq::moldudp64_session<pmd_handler>(data);
 }
diff --git a/tests/order_book_perf_test.cc b/tests/order_book_perf_test.cc
index d12d02a..91bc707 100644
--- a/tests/order_book_perf_test.cc
+++ b/tests/order_book_perf_test.cc
@@ -2,7 +2,7 @@
 #include <iostream>
 #include <chrono>
 
-using namespace helix::core;
+using namespace helix;
 
 using clock_type = std::chrono::high_resolution_clock;